JP5861997B2 - DC / DC conversion circuit - Google Patents

Description

  The present invention relates to a DC / DC conversion circuit, and more particularly to a circuit for boosting a direct current voltage.

  FIG. 7 is a basic circuit of a conventional step-up chopper 100 (see, for example, Non-Patent Document 1). In the figure, when switching element Q is turned on, a current flows from DC power supply 200 to reactor L, and energy is stored in reactor L. Next, when the switching element Q is turned off, the energy stored in the reactor L is released to the output side, and a voltage higher than the power supply voltage of the DC power supply 200 appears across the capacitor C via the diode D. The switching element Q is PWM-controlled by a control device (not shown), and the duty is adjusted so that a desired output voltage can be obtained.

Arte 21 “Power Electronics” 1st edition (issued in 1999), page 68, Ohmsha

In the conventional step-up chopper 100 as described above, the reactor L is a relatively large component, which is a factor that hinders downsizing. Further, the reactor L has a copper loss of the coil and an iron loss of the iron core, and therefore, conversion efficiency of DC / DC conversion by boosting is impaired.
In view of such conventional problems, an object of the present invention is to realize downsizing and improvement in conversion efficiency in a boosting DC / DC conversion circuit.

(1) The present invention is a DC / DC conversion circuit that boosts and outputs an input DC voltage, a circuit that connects a plurality of capacitors in parallel with each other via a switch for parallel connection, and It includes a circuit that connects each capacitor in series via a switch for series connection.By selecting ON or OFF of each switch, each capacitor connected in parallel is charged with the input voltage and then connected in series. And a connection device that repeats the process of switching and discharging the voltage appearing at both ends of the series body of the plurality of capacitors as an output voltage. Here, for example, one of the plurality of capacitors is always connected in parallel with the DC power source in the process.

In the DC / DC conversion circuit configured as described above, the capacitors charged in the parallel connection state are switched to the serial connection, so that the voltage output by the discharge is the sum of the voltages across the capacitors. That is, the input voltage is basically multiplied by the number of capacitors and boosted. Such a DC / DC conversion circuit does not require a reactor for boosting .

( 2 ) The DC / DC conversion circuit according to (1) further includes a smoothing capacitor that smoothes the discharge output connected in series, and an output switch that is inserted in a circuit that reaches the smoothing capacitor. Preferably it is.
In this case, by turning off the output switch, the smoothing capacitor, that is, the output side, can be isolated from the capacitor and the input voltage in parallel connection.

In the DC / DC conversion circuit of (1) above, a plurality of capacitors and connection devices may be provided in a single stage, and the structure may be provided in a plurality of stages.
In this case, the input voltage can be boosted to a higher voltage by boosting it in a plurality of stages.

(3) Further, in the DC / DC converter circuit of the upper SL have Zureka, switches, SiC semiconductor, GaN semiconductor, or may be a switching element consisting of a diamond semiconductor.
These devices have an overwhelmingly superior dielectric strength compared to silicon, and have low switching loss due to their low on-resistance. Also suitable for high-speed response and excellent durability.

  According to the DC / DC conversion circuit of the present invention, downsizing is possible and the conversion efficiency is improved.

1 is a diagram illustrating a main configuration of a DC / DC conversion circuit according to a first embodiment of the present invention. Regarding the DC / DC conversion circuit shown in FIG. 1, (a) and (b) are circuit diagrams showing the states of the switches when the capacitor is charged and discharged, respectively. It is an example of the time chart regarding ON / OFF of each switch shown in FIG. 1 or FIG. It is a figure which shows the main structures of the DC / DC conversion circuit which concerns on 2nd Embodiment of this invention. It is an example of the time chart regarding ON / OFF of each switch shown in FIG. FIG. 2 is an example of a circuit diagram in the case where the switch in FIG. This is a basic circuit of a conventional boost chopper.

<< First Embodiment >>
FIG. 1 is a diagram showing a main configuration of a DC / DC conversion circuit according to the first embodiment of the present invention. In the figure, a DC voltage is input to a DC / DC conversion circuit 1 from a DC power supply 2. The DC power source 2 is a power source that rectifies an AC voltage or a power source that uses a battery.

  The DC / DC conversion circuit 1 includes a plurality of capacitors C1 to C4 and a connection device 10 (not including the capacitors C1 to C4) for connecting these capacitors C1 to C4 in parallel or in series. As an element. The connection device 10 includes a circuit (horizontal line in the figure) for connecting the capacitors C1 to C4 in parallel via switches S1a, S2a, S3a, S1b, S2b, and S3b for parallel connection, and a switch for series connection. A circuit (line in the oblique direction in the figure) for connecting the capacitors C1 to C4 in series via S1c, S2c, and S3c is included.

  Also, an output smoothing capacitor Cout is connected between a node (connection point) Np and Nn on the circuit via an output switch Sout. The voltage across the smoothing capacitor Cout becomes the output voltage of the DC / DC conversion circuit 1.

  The switches S1a, S2a, S3a, S1b, S2b, S3b, S1c, S2c, S3c, and Sout are on / off controlled by a control device 11 including a microcomputer and a switching driver. The number of capacitors shown (four) is merely an example for convenience of explanation, and the number varies depending on the relationship between the input voltage and the desired output voltage. The capacitances of the capacitors C1 to C4 do not necessarily have to be a common value, but are typically the same value.

  As the switch, a switching element made of a SiC semiconductor, a GaN semiconductor, or a diamond semiconductor is suitable. These elements have overwhelmingly superior dielectric strength compared to silicon, and can withstand a voltage of 1000 V or higher with a low on-resistance. Switching loss can be reduced by the low on-resistance. Also suitable for high-speed response and excellent durability.

Next, the operation of the DC / DC conversion circuit 1 configured as described above will be described. FIGS. 2A and 2B are circuit diagrams showing the state of the switches when charging and discharging the capacitors C1 to C4, respectively.
First, at the time of charging, the control device 11 (FIG. 1) turns on all the switches S1a, S2a, S3a, S1b, S2b, S3b for parallel connection as shown in FIG. The switches S1c, S2c, S3c and the output switch Sout are turned off.

  In this state, the four capacitors C1 to C4 connected in parallel to each other are charged by the input voltage Vin supplied from the DC power supply 2, and the both-end voltages have the same value Vin. Even if the capacitances of the four capacitors C1 to C4 are not completely the same, charges corresponding to the respective capacitances are accumulated, and the voltages at both ends have the same value Vin.

Next, as shown in (b), the control device 11 turns off all the switches S1a, S2a, S3a, S1b, S2b, S3b for parallel connection and switches S1c, S2c, S3c and the output switch Sout are turned on. As a result, the four capacitors C1 to C4 are connected in series. At this time, the voltage Vout generated between the nodes Np and Nn is the sum of the voltages across the capacitors C1 to C4 connected in series in a short time,
Vout = 4 · Vin
It becomes. If the number of capacitors is n (a natural number of 2 or more), in general, Vout = n · Vin
It is expressed.

  FIG. 3 is an example of a time chart regarding ON / OFF of each switch. For example, the switches S1a, S2a, S3a, S1b, S2b, and S3b for parallel connection are turned on at time t1, and are turned off at time t2. Immediately after that, at time t3, the series connection switches S1c, S2c, S3c and the output switch Sout are turned on, and at time t4, they are turned off. Similarly, switching is repeated at the period T. A slight time difference (for example, t2 to t3) is provided between the switch for parallel connection and the switch for series connection so that they are not turned on at the same time.

  In this way, the charging of the capacitors C1 to C4 shown in FIG. 2A and the discharging of the capacitors C1 to C4 shown in FIG. 2B are repeatedly performed at a high frequency of about 2 kHz, for example. That is, the connection device 10 appropriately switches on or off each switch to charge each of the capacitors C1 to C4 connected in parallel with the input voltage, and then switches to a serial connection and outputs the discharge. Repeat the process. Therefore, the capacitors C1 to C4 function as a DC power supply without exhausting energy, and the voltage Vout is output from both ends of the smoothing capacitor Cout. That is, the DC / DC conversion circuit 1 boosts the input voltage four times (n times).

  As an example of specific numerical values, the capacitance of the capacitors C1 to C4 is 4000 μF, the voltage at both ends during charging is 25 V, the capacitance of the smoothing capacitor Cout is 1000 μF, the output voltage Vout is 100 V, and a current of 10 A is loaded. The output fluctuation of the voltage Vout can be suppressed to about −5% (95 to 100 V) by switching at 2 kHz.

  As described above, in the DC / DC conversion circuit 1, the capacitors charged in the parallel connection state are switched to the serial connection, so that the voltage output by the discharge is the sum of the voltages at both ends of each capacitor. That is, the input voltage is basically multiplied by the number of capacitors and boosted. Since such a DC / DC conversion circuit 1 does not require a reactor for boosting, it is suitable for miniaturization and weight reduction, and since there is no copper loss / iron loss of the reactor, the conversion efficiency is improved.

  Since the output switch Sout is inserted in the circuit leading to the smoothing capacitor Cout, if the switch Sout is turned off, the smoothing capacitor Cout, that is, the output side capacitor is connected in parallel with a different voltage. It can be isolated from C1 to C4 and the input voltage Vin.

<< Second Embodiment >>
FIG. 4 is a diagram showing a main configuration of the DC / DC conversion circuit 1 according to the second embodiment of the present invention. In this case as well, a control device 11 is provided as in FIG. 1, but is not shown here.

  The essential difference from the first embodiment is that “a plurality of capacitors and connection devices” are configured in one stage, and the configuration is provided in a plurality of stages (in this example, two stages). Here, the number of capacitors in each stage is three, but this is merely an example for convenience of explanation, and the number varies depending on the relationship between the input voltage and the desired output voltage.

  First, the first-stage booster circuit 101 is a circuit for connecting the capacitors C11 to C13 in parallel via three capacitors C11 to C13 and switches S11a, S12a, S11b, and S12b for parallel connection (the horizontal direction in the figure). And a circuit (line in the oblique direction in the figure) for connecting the capacitors C11 to C13 in series via switches S11c and S12c for series connection.

  Further, the second-stage booster circuit 102 is a circuit for connecting the capacitors C21 to C23 in parallel via three capacitors C21 to C23 and switches S21a, S22a, S21b, and S22b for parallel connection (the horizontal direction in the figure). And a circuit for connecting the capacitors C21 to C23 in series via the series connection switches S21c and S22c (oblique lines in the figure).

  The high-potential side node Np1 at the time of discharging in the first stage booster circuit 101 is connected to the charging voltage application node Npc in the second stage booster circuit 102 via the output switch So1 of the first stage booster circuit 101. Connected to. Further, the output booster circuit 102 has an output switch So2 between the high potential side node Np2 and the negative circuit side node Nn2 during discharge in the second stage booster circuit 102. A smoothing capacitor Cout is connected. The voltage across the smoothing capacitor Cout becomes the output voltage of the DC / DC conversion circuit 1.

Next, the operation of the DC / DC conversion circuit 1 according to the second embodiment configured as described above will be described.
First, at the time of charging in the first-stage booster circuit 101, the control device 11 (FIG. 1) turns on all the switches S11a, S12a, S11b, S12b for parallel connection and switches S11c, S12c and the output switch So1 are turned off.

  In this state, the three capacitors C11 to C13 connected in parallel to each other are charged by the input voltage Vin supplied from the DC power supply 2, and the both-end voltages have the same value Vin. Even if the capacitances of the three capacitors C11 to C13 are not completely the same, charges corresponding to the respective capacitances are accumulated, and the voltages at both ends have the same value Vin.

Next, the control device 11 turns off all the parallel connection switches S11a, S12a, S11b, and S12b, and turns on the series connection switches S11c and S12c and the output switch So1. As a result, the three capacitors C11 to C13 are connected in series. At this time, the voltage Vo1 generated between the nodes Np1 to Nn1 is the sum of the voltages across the capacitors C11 to C13 connected in series in a short time,
Vo1 = 3 · Vin
It becomes. If the number of capacitors is n (a natural number of 2 or more), generally Vo1 = n · Vin
It is expressed.

  The charging and discharging of the capacitors C11 to C13 related to the first stage booster circuit 101 are repeatedly executed at a high frequency of about 2 kHz, for example. In other words, the connection device 10 appropriately switches on or off each switch to charge each of the capacitors C11 to C13 connected in parallel with the input voltage, and then switches to a serial connection and outputs the discharge. Repeat the process. Therefore, the capacitors C11 to C13 function as a DC power supply without exhausting energy, and the voltage Vo1 is output between the nodes Np1 to Nn1.

  On the other hand, when the discharge output is performed from the first-stage booster circuit 101, the control device 11 turns on all the switches S21a, S22a, S21b, S22b for parallel connection in the second-stage booster circuit 102, and The switches S21c and S22c for series connection and the switch So2 for output are turned off.

  In this state, the three capacitors C21 to C23 connected in parallel with each other are charged by the input voltage Vo1 supplied from the first-stage booster circuit 101, and the both-end voltages have the same value Vo1. Even if the capacitances of the three capacitors C21 to C23 are not completely the same, electric charges corresponding to the respective capacitances are accumulated, and the both-end voltages are the same value Vo1.

Next, the control device 11 turns off all the parallel connection switches S21a, S22a, S21b, and S22b, and turns on the series connection switches S21c and S22c and the output switch So2. As a result, the three capacitors C21 to C23 are connected in series. At this time, the voltage Vo2 generated between the nodes Np2 and Nn2 is the sum of the voltages across the capacitors C21 to C23 connected in series in a short time,
Vo2 = 3 ・ Vo1 = 9 ・ Vin
It becomes. If the number of capacitors in the booster circuit 101 is n and the number of capacitors in the booster circuit 102 is m (a natural number of 2 or more), generally, Vo2 = m · Vo1 = m · n · Vin
It is expressed.

  The charging and discharging of the capacitors C <b> 21 to C <b> 23 regarding the second stage booster circuit 102 are repeatedly executed at a high frequency as in the first stage booster circuit 101. That is, the connection device 10 appropriately switches on or off each switch to charge the capacitors C21 to C23 connected in parallel with the input voltage, and then switches to a serial connection and outputs the discharge. Repeat the process. Therefore, the capacitors C21 to C23 function as a DC power supply without exhausting energy, and the voltage Vo2 is output between the nodes Np2 and Nn2.

  FIG. 5 is an example of a time chart regarding ON / OFF of each switch in the DC / DC conversion circuit 1 of FIG. For example, the switches S11a, S12a, S11b, and S12b for parallel connection in the first-stage booster circuit 101 are turned on at time t1, and turned off at time t2. In parallel with this, the series connection switches S21c and S22c and the output switch So2 in the second stage booster circuit 102 are turned on at time t1, and turned off at time t2.

At time t3, the series-connected switches S11c and S12c and the output switch So1 in the first-stage booster circuit 101 are turned on, and are turned off at time t4. In parallel with this, the switches S21a, S22a, S21b, S22b for parallel connection in the second step-up circuit 102 are turned on at time t3 and turned off at time t4.
Similarly, switching is repeated at the period T. A slight time difference (for example, t2 to t3) is provided between the switch for parallel connection and the switch for series connection so that they are not turned on at the same time.

As described above, the DC / DC conversion circuit 1 according to the second embodiment does not require a reactor for boosting, as in the first embodiment, and thus is suitable for downsizing, and the copper loss and iron loss of the reactor are reduced. Since there is no conversion efficiency is improved.
Further, by providing the booster circuit (multiple capacitors + connector) in such a plurality of stages, the input voltage can be boosted in a plurality of stages, which is a higher voltage than in the case of the first embodiment. Can be boosted to

<Others>
In the case where the switch in FIG. 1 is constituted by, for example, a MOS-FET, it can be constituted, for example, as shown in FIG. Since the MOS-FET usually has a parasitic diode inside, it is necessary to consider the arrangement of the drain and the source. In the parallel connection switches S1a, S2a, S3a, S1b, S2b, and S3b, when the capacitors C1 to C4 are connected in series (that is, when the parallel connection switch is off), the parasitic diode does not become forward with respect to the potential difference. Are arranged as follows.

  Similarly, the switch for series connection may be arranged so that the parasitic diode does not become forward with respect to the potential difference when the capacitors C1 to C4 are connected in parallel (that is, when the switch for series connection is OFF). As shown in the figure, each pair may be arranged in series so as to face each other with opposite polarity. The three pairs of switches (S1c1, S1c2), (S2c1, S2c2), and (S3c1, S3c2) are simultaneously turned on / off, and when they are off, current is prevented in both directions by opposing parasitic diodes.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Since the DC / DC conversion circuit of the present invention is compact and has high conversion efficiency, it can be used for various DC boosting applications. For example, it can be used for a solar power generation system. That is, in the photovoltaic power generation system, it is necessary to boost the power generation voltage of the solar cell module that fluctuates according to the sunshine conditions. Can do.

1: DC / DC conversion circuit 10: connection devices C1 to C4, C11 to C13, C21 to C23: capacitor Cout: smoothing capacitors S1a, S2a, S3a, S1b, S2b, S3b, S1c, S2c, S3c, S11a, S12a , S11b, S12b, S21a, S22a, S21b, S22b, S11c, S12c, S21c, S22c, S1c1, S1c2, S2c1, S2c2, S3c1, S3c2, Sout, So1, So2: switch

Claims (3)

A DC / DC conversion circuit that boosts and outputs a DC voltage input from a DC power source ,
A plurality of capacitors;
Including a circuit for connecting each capacitor in parallel via a switch for parallel connection, and a circuit for connecting each capacitor in series via a switch for series connection, the parallel connection by selecting on or off of each switch And a connection device that repeats the process of charging each of the capacitors that has been input with the input voltage and then switching to a serial connection to discharge and output the voltage appearing at both ends of the series body of the plurality of capacitors as an output voltage. ,
One of the plurality of capacitors is a DC / DC conversion circuit that is always connected in parallel with the DC power source in the step . 2. The DC / DC conversion circuit according to claim 1, further comprising: a smoothing capacitor that smoothes the series-connected discharge output; and an output switch that is inserted in a circuit that reaches the smoothing capacitor . The DC / DC conversion circuit according to claim 1, wherein the switch is a switching element made of a SiC semiconductor, a GaN semiconductor, or a diamond semiconductor .

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